1. Field of the Invention
The invention relates generally to ceiling fans and ceiling fan motors. More particularly, the present invention relates to ceiling fan motors which operate under significantly reduced temperatures through the use of forced air ventilation arrangements that enable air to be forced through the motor casing, and through the use of conductive and convective heat dissipation arrangements to enable improved heat transfer through the motor components. The present invention also relates to an integrally cast ceiling fan motor preferably of cast aluminum, enabling tighter motor component tolerances, lower manufacturing costs, and easier assembly.
2. Description of Related Art
Electric motors are widely used in a variety of consumer products. One common type of electric motor includes a rotor which is attached to a shaft mounted within the end covers of a motor casing. The rotor typically is made of a stack of electrical steel lamination and may be die cast or wound, depending upon the type of motor. Bearings, such as ball bearings or sleeve bearings located at opposite ends of the shaft, are held in place within the end covers by stationary bearing retainers which are fixed to the end covers to enable the rotor and rotor shaft to rotate with respect to the casing of the motor. Surrounding the rotor is a stator where the windings of the motor are located. The stator is normally a stack of electrical steel lamination. As is well known, the rotor is oriented centrally within the stator and rotates with respect to the stator.
In another type of motor, generally known as an inside-out motor, the location of the rotor and stator are reversed. That is, the rotor is positioned outside of the stator and is sandwiched between, and attached to, two end covers that define the motor casing. Bearing retainers also are provided for the inside-out motor and are secured to the top and bottom end covers to rotate therewith.
A problem common to electric motors in general is the heat build-up that takes place during routine motor operation. High temperature heat build-up is a well-known undesirable resultant in electric motor operation and considerable efforts have been undertaken over the years to try to reduce the motor operating temperatures by cooling the motor during motor operation.
In electric motors of the type where the rotor lies within the stator, internal fan or impeller arrangements have been provided in an attempt to cool the stator windings and to pump the heat out of the motor. The fan may include blades mounted on the shaft of the rotor itself, within the motor casing. The fan may include fin-like blades molded directly to the rotor end rings whereby rotor shaft rotation rotates the blades to provide a fan-like effect during motor operation.
In the case of an inside-out motor, providing a cooling fan of the types described above for conventional motors has not been practical. Because the shaft of the motor, which is mounted to the stator, does not rotate, obviously any fan blades mounted on the shaft will not rotate and the cooling effect will be unavailable. Providing fins or blades on the surrounding rotor has proven to be of little help in increasing air circulation inside the motor, i.e., to the motor windings on the stator, because the rotor is outside of the stator.
Electric motors of the inside-out type are commonly used in electric ceiling fans. Most modern ceiling fans include an inside-out electric motor suspended from the ceiling through the stator shaft. The motor casing, which typically is formed from upper and lower end covers, or end bells, to which the rotor is affixed, rotates about the stator. A plurality of ceiling fan blades are mounted to either the top or bottom surface of the motor casing by means of blade irons, as shown in U.S. Pat. No. 5,462,412, or through the use of separate blade ramp components such as those disclosed in U.S. Pat. No. 5,222,864. Conventional ceiling fans also generally are provided with one or more electrical switches for controlling both the speed and the rotational direction of the motor. The electrical switches are typically located within a switch housing that is disposed beneath the motor. Additionally, many ceiling fans include light fixtures mounted to the underside of the switch housing. The overall motor casing is typically covered by a motor housing or cover for aesthetic purposes.
Electric motor heat build-up poses a particular problem within ceiling fans. Prior attempts to cool the stator windings and the rotor in inside-out motors within ceiling fans include providing ventilation holes within the motor casing end covers to improve the circulation of air within the motor casing. However, in reality, very little air circulation takes place because the presence of the stator itself forms an obstruction in the air flow paths. Ventilation holes also have been provided in the stator to provide a path for the cross-flow of air between the ventilation holes within the motor casing end covers, but the air flow is generally inadequate due to a number of factors that are unique to the ceiling fan motor environment.
For example, a ceiling fan motor and motor casing are typically surrounded by an outer motor housing. The motor housing forms a shield around the motor which obstructs the flow of air into the ventilation holes provided in the motor casing and around and through the motor itself. In addition, inadequate air flow results from the very nature of the ceiling fan blade design. The circulation of air in a room is caused by rotation of the fan blades. Since the circulation of air takes place at the tips of the blades, a void is created in the center of the fan which restricts the flow of air in the center region precisely where the motor housing is mounted.
The high heat build-up within the electric motors used in ceiling fans may significantly reduce the life of the motor and undesirably affect motor performance. Thus, there is a clear need for an electric motor of the inside-out type for use with ceiling fans which has substantially reduced operating temperatures to extend the operating life of the motor and enable a more powerful motor design.
Another problem typically encountered in ceiling fan motors is the imperfect alignment among the various motor components which results not only in increased wear but in undesirable noise and vibration levels. Electric motors of the type used in ceiling fans include several separate and distinct motor components that are assembled together through conventional screws or bolt and nut arrangements. These motor components include a separate rotor which is secured to the separate upper and lower motor casing end covers. Each of these components must precisely fit together, and with respect to the stator, at relatively close tolerances. However, manufacture of these components typically requires separate machining operations on separate components which then need to be assembled together. The separate machining operations limit the ability to achieve the desirable tight tolerances. Moreover, the manufacturing and assembly costs may be substantial. Thus, there is a need for an electric motor for a ceiling fan, particularly an inside-out electric motor for a ceiling fan, that may be easily and economically manufactured to tight tolerances to provide reduced vibrations and noise and a longer motor life.
Another problem in conventional ceiling fan designs is the assembly of the ceiling fan blades to the motor casing. Because the fan blades are relatively large in size, and because ceiling fans are adapted for use with several different types of fan blade arrangements, the mounting of the blades to the ceiling fan motor is typically accomplished by the retailer or sometimes even the consumer. This blade mounting requires the assembly of either blade irons or separate blade ramps to the ceiling fan motor casing. These steps in mounting the blade irons and/or the blade ramps to the motor casing are time consuming and expensive. Thus, a need has arisen to enable the mounting of fan blades to ceiling fan motor casings without the use of separate blade ramp and/or blade iron attachment components.